THE CRYSTAL STRUCTURE OF Ag3Ca5

Abstract

Ag3Ca5 is tetragonal, a = 8.039 ± 5 Å, c = 15.011 ± 15 Å, c/a = 1.87, space group I4/mcm. The structure is of the D8l type with 4 AgI in 4(a); 8 AgII in 8(h), x = 0.378 ± 5; 4CaI in 4(c); and 16 CaII in 16(l), x = 0.164 ± 5 and z = 0.150 ± 5. The structure is characterized by sheets of closely linked Ag and Ca atoms parallel to (001). An indexed powder pattern is given. NH4Pb2Br5, RbPb2Br5, and KPb2Br5 also have the same structure and should be included together with B3Cr5, Ge3Ta5, Si3Ta5, and Si3Nb5 in the D8l group.